Although this invention is applicable to numerous and various types of linkages for throttle control of internal combustion engines, it has been found to be particularly useful in the environment of diesel engines for heavy vehicles. Therefore, without limiting the applicability of the invention to "throttle control linkage for internal combustion engines, particularly diesel engines", the invention will be described in such environment.
It is well known that in the manufacture of fuel injector pumps the amount of travel of the injector lever from the idle or low or LI position to the full throttle or high idle or HI position varies among fuel injector pumps of the same model. At the factory, a stop mechanism is located and locked at one end of the travel of the injector lever to designate the idle or low idle or LI position of the injector lever on the fuel injector pump. Another stop mechanism is located and locked at the other end of the travel of the injector lever to designate the full throttle or high idle or HI position of the injector lever on the fuel injector pump. The end of travel positions are determined based upon the required output specifications of the fuel injector pump at the two end positions. Unfortunately, these two end positions usually vary among different fuel injector pumps of the same model so the length of travel of the injector lever varies among the fuel injector pumps.
When a fuel injector pump is installed for operation with a diesel engine, the throttle control linkage must be operatively connected between the throttle control lever and the pivotally-mounted injector lever on the fuel injector pump. Earlier attempts to solve the problem of the variable length of injector lever travel among fuel injector pumps have resulted in two types of solutions.
One solution is to provide an adjustable stop on the throttle control lever. The linkage ratio or the ratio of the travel between the throttle control lever and the injector lever is made constant. The injector lever is positioned against the stop at the HI or full throttle position and the throttle control lever is positioned to its HI or full throttle position. All the links or portions of the throttle control linkage between the injector lever and the throttle control lever are operatively attached together to form a complete linkage. The throttle control lever is then moved toward its LI or low idle position until the injector lever hits the stop at its LI or low idle position. At this point, a physical stop 12 is installed to prevent any further motion of the throttle control lever 10 past the low idle position of the injector lever, as shown in FIG. 1. This results in the travel of the throttle lever being dependent upon and limited by the travel of the injector lever. Often, the resulting travel of the throttle control lever is too short for good control of engine speed.
Another solution provides for making the linkage ratio adjustable by placing several holes 14 (see FIG. 2) about some nominal location in one or more bellcranks 16 in the throttle control linkage. This may be accomplished at the throttle lever bellcrank or at some intermediate bellcrank. The additional holes 14 are located so as to give the expected range of linkage ratios required to account for injector lever travel variation. This particular solution requires that the linkage be connected using a nominal hole as a starting point. By trial and error, the hole giving the closest desired full travel of the injector lever is found. This type of linkage can only give incremental travel variations and requires disconnecting a link or portion of the throttle control linkage, adjusting the length of the link and reconnecting the linkage in a new hole for each trial and error iteration. Accurate adjustment of engine idle speed from LI to HI cannot always be made because only certain distinct ratio's are available as governed by the number and spacing of holes 14.